Motor air flow cooling

ABSTRACT

In one possible embodiment, an aircraft electric motor cooling system is provided having an airflow path through a spinner which includes a first airflow path between an inner rotor and a stator, a second airflow path between an outer rotor the stator and a third airflow path along an outer surface of the outer rotor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the following applicationswhich are all herein incorporated by reference in their entireties:

-   -   U.S. Provisional Application No. 61/194,098, filed Sep. 23,        2008, by Daboussi, entitled WINDING DESIGN FOR IRONLESS P.M.        MOTOR;    -   U.S. Provisional Application No. 61/194,099filed Sep. 23, 2008,        by Daboussi et al, entitled PROPELLER DRIVE UNIT FOR HALE UAV;        and    -   U.S. Provisional Application No. 61/194,056, filed Sep. 23,        2008, by Hibbs, entitled FLUX CONCENTRATOR FOR IRONLESS MOTORS.

The present application is also related to the following applications,which are hereby incorporated by reference in their entireties:

-   -   U.S. Non-provisional application Ser. No. 12/565,705, filed Sep.        23, 2009, entitled COMPRESSED MOTOR WINDING, by Daboussi et al;    -   U.S. Non-provisional application Ser. No. 12/565,710 filed Sep.        23, 2009, entitled STATOR WINDING HEAT SINK CONFIGURATION, by        Daboussi et al; and    -   U.S. Non-provisional application Ser. No. 12/565,718 filed Sep.        23, 2009, entitled FLUX CONCENTRATOR FOR IRONLESS MOTORS, by        Hibbs.

BACKGROUND

Electric motors for vehicles need to have high efficiency to conservepower. Furthermore, in unmanned aerial vehicles, light weight andcompact electric motors are also desirable. Thus, ironless motors areoften used which can provide the benefit of no iron losses due tochanging flux direction.

Motors are normally rated for the peak power and efficiency of themotor. In some applications, high part load efficiency is desired, whichis high efficiency when machine is loaded at a partial load, i.e. 15% orsome other percent.

What is needed is a higher efficiency compact motor.

SUMMARY

In one possible embodiment, an aircraft electric motor cooling system isprovided having an airflow path through a spinner which includes a firstairflow path between an inner rotor and a stator, a second airflow pathbetween an outer rotor the stator and a third airflow path along anouter surface of the outer rotor.

In various embodiments, the first airflow path extends along inner rotormagnets and/or the second airflow path extends along outer rotormagnets. In various embodiments, the first airflow path extends along afront stator yoke and along a rear stator yoke and/or the second airflowpath extends along a front stator yoke and a rear stator yoke.

In various embodiments, the second and third airflow paths extendthrough a rear stator heat sink along with an air stream path. Invarious embodiments, the airflow path extending through the spinnercomprises a portion extending through front stator cooling fins, andwherein the second and third portion are derived at least in part fromthe front stator cooling fins portion.

Other embodiments are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be betterunderstood with regard to the following description, appended claims,and accompanying drawings where:

FIG. 1 shows a simplified exploded perspective view of an example motor.

FIG. 2 shows a simplified cross sectional side view of the motor of FIG.1 along its longitudinal axis.

FIG. 3 shows a simplified perspective view of the stator having awinding.

FIG. 4 shows a simplified view along a cross section of the motor ofFIG. 2.

FIG. 5 shows a simplified front view of the motor.

DESCRIPTION

FIG. 1 shows a simplified exploded perspective view of an example motor10 along axis 22. A stator 40 is secured to a housing 60. Inner rotor 50and outer rotor 30 are secured to each other and surround the stator 40.An optional propeller hub 75, into which propeller blades 70 aremounted, is secured to the inner rotor 50. The propeller hub 75rotatably mounts on the shaft 65 with bearings 16 and 18. The bearings16 and 18 are retained by retainers 20 and 14 and cover 12.

FIG. 2 shows a simplified cross-sectional side view of the motor 10 ofFIG. 1 along its longitudinal axis 22. The stator 40 is located betweenmagnets 35 and 55 of the inner and outer rotors 50 and 30, respectively.The shaft 65 may be fabricated of carbon fiber or other suitablematerial.

FIG. 3 shows a simplified perspective view of the stator 40 having awinding 45. The winding 45 is encased within the stator 40. Cooling fins42 and 44 are bonded to the front and back stator yoke portions 43 f and43 b, respectively. FIG. 3 shows one air flow cooling path, indicated bythe arrow 301, through the cooling fins 42 and 44.

FIG. 4 shows a simplified cross section of the motor 10 of FIG. 2. Thewinding 45 has a compressed central region 45 c. The winding 45 iscompressed in the central region 45 c so that more conductor material ofthe winding 45 can be placed between the magnets 35 and 55 and so thatmore conductor can be located closer to the magnets 35 and 55 of therotors 30 and 50 to provide increased magnetic field strength in thewinding 45. In this embodiment, it is not necessary that the ends 45 eof the winding 45 also be compressed. This is because the ends 45 e ofthe winding 45 do not pass between the magnets 35 and 55 of the rotors30 and 50.

In accordance with various embodiments, for both axial and radialironless P.M. or permanent magnet machines, the winding 45 should have ahigh packing density to minimize I²R losses and a construction thatminimizes eddy losses. The magnets 35 and 55 in the rotor 40 passover/under a central active region 45 c of the stator winding 45, andnot over/under the edges 45 e of the stator winding 45. Thus, in variousembodiments, the active region 45 c of the winding 45 should have asmuch conductor, i.e. copper, as possible in the volume of the activeregion 45 c.

Also, in various embodiments, the winding 45 should have high rigidityso that the winding 45 does not deflect and contact the magnets 35 or55, and to adequately withstand the turn-to-turn voltages and associatedforces. The winding 45 is enclosed in a suitable material, such asepoxy.

Although shown large for illustration purposes, the air gaps 49 u and 49i between the stator 40 and the magnets 35 and 55 are small so that themagnets 35 and 55 provide the maximum magnetic field in the winding 45.The close proximity of the stator 40 with the magnets 35 and 55,however, can facilitate unwanted heat transfer from the stator 40 to themagnets 35 and 55 across the gaps 49 u and 49 i. As excessive heat candamage the magnets 35 and 55, the stator 40 is provided with front andback cooling fins 42 and 44.

Thus, the winding 45 should have a low thermal impedance path to thecooling fins 42 and 44. For most embodiments, the winding 45 is encasedin epoxy mixed with a thermally conductive filler such as aluminumoxide, boron nitride, or other material that facilitates heatconduction.

The front stator yoke 43 f surrounds the front end 40 e _(f) of thestator 40 on three sides to provide more surface area for heat transferout of the stator 40 into the front stator yoke 43 f. Similarly, theback yoke 43 b surrounds three sides of the back end 40 e _(b) of thestator.

The cooling fins 42 and 44 may be made of aluminum or other suitablelightweight heat conductive material. The cooling fins 42 and 44 may beformed separately and bonded with a low thermal impedance bond to thestator yokes 43 f and 43 b, or integrally formed with them. Further itis possible in some embodiments that the front end 40 e _(f) of thestator 40 and the back end 40 e _(b) be directly connected to thecooling fins 42 and 44, respectively.

The front cooling fins 42 extend away in a forward direction from thefront surface 43 f ₁ of the front stator yoke 43 f. The front coolingfins 42 are radially oriented with respect to the axis 22 (FIG. 2). Theback surface 42 b of the cooling fins 42 are bonded to the front surface43 f ₁ of the front stator yoke 43 f. The front surface 42 f of frontcooling fins 42 is solid such that the air flows radially outwardthrough the front cooling fins 42 with respect to the axis 22 (FIG. 2).In another embodiment not shown, the solid front surface 42 f is notpresent. In still another embodiment not shown, the front fins areoriented radially, with air flow axially between them instead of radialair flow. Other configurations are possible.

The rear cooling fins 44 surround the back stator yoke 43 b and areradially oriented with respect to the axis 22 (FIG. 2). The rear coolingfins 44 are surrounded by a solid outer ring 44 o. The inner surface(s)44 i, which may be a bent over portions of each of the fins 44, isbonded to the top outer surface 43 b _(t) of the back stator yoke 43 b.The air flows through the rear cooling fins 44 in a direction generallyalong an axis parallel with the axis 22 (FIG. 2).

Air flow 401 enters through the optional spinner 80 and cover 33. Asmall portion 401 d of the air flow 401 passes between the inner magnets55 and the stator 40 through gap 49 i, cooling both the inner magnets 55and the stator 40, as well as portions of the front yoke 43 f and theback yoke 43 b, directly by convection. This small portion 401 d exitsthrough ports 48 (shown in FIGS. 2-4) in the back stator yoke 43 b. Mostof the air flow 401 passes through the front cooling fins 42 asindicated by air flow arrow 401a. After passing through the frontcooling fins 42, a small portion 401 b of air flow 401 a passes betweenthe upper magnets 35 and the stator 40 through the gap 49 u, cookingboth, the outer magnets 35 and the stator 40, as well as portions of thefront yoke 43 f and the back yoke 43 b, directly by convection.

A large portion 401 c of the air flow 401 b is diverted by the cover 33and the spinner 80 to pass through port (also shown in FIGS. 1 and 2) toflow over the outer rotor 30. Depending on the embodiment, a smallportion 401 g of the air flow 401 may also flow in front of the frontcooling fins 42 and exit through port 38. The large portion 401 ccombines with the air flow 401 b from the upper gap 49 u to flow 401 fthrough the rear cooling fin 44, along with airflow 401 e enteringdirectly from the air stream adjacent to the spinner 80.

In one embodiment, the combination of the cooling fin size andplacement, along with the air flow over and through the components asdescribed herein is such that the magnets are maintained at atemperature below about 70 degree Celsius and the winding is maintainedat a temperature below about 80-90 degrees Celsius.

FIG. 5 shows a simplified front view of the motor 10. The inner andouter rotors 50 and 30 are held together in this embodiment with threebrackets 32, which also hold on an annular cover 33 (FIGS. 2 and 4). Theair flow 401 a for the front cooling fins 42 flows through theseparations between the three brackets 32. Open area for airflow 401(FIG. 4) is about 80% of the total available area, the remaining 20% isblocked by the brackets 32. Airflow 401 then flows through theseparations, with most of the air flow 401 a flowing through the frontcooling fins 42. The air flow 401 is slowed by the spinner 80 (FIGS. 2and 4) and fins 42 so that little flow energy is lost, thenre-accelerated to free air stream velocity at port 38.

Although show in the context of aircraft, embodiments of the inventionare not limited to aircraft. Further not all parts are required in allembodiments. The above described apparatuses, methods, and systems arenot limited to UAVs, or aircraft. Various implementations and/orembodiments may include other motor uses, i.e. auto, industrial, etc.Further in some embodiments, the airflow may be generated, or it may bethe result of motion, i.e. flying, driving, etc., of the apparatus orsystem.

It is worthy to note that any reference to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment may beincluded in an embodiment, if desired. The appearances of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment.

The illustrations and examples provided herein are for explanatorypurposes and are not intended to limit the scope of the appended claims.This disclosure is to be considered an exemplification of the principlesof the invention and is not intended to limit the spirit and scope ofthe invention and/or claims of the embodiment illustrated.

Those skilled in the art will make modifications to the invention forparticular applications of the invention.

The discussion included in this patent is intended to serve as a basicdescription. The reader should be aware that the specific discussion maynot explicitly describe all embodiments possible and alternatives areimplicit. Also, this discussion may not fully explain the generic natureof the invention and may not explicitly show how each feature or elementcan actually be representative or equivalent elements. Again, these areimplicitly included in this disclosure. Where the invention is describedin device-oriented terminology, each element of the device implicitlyperforms a function. It should also be understood that a variety ofchanges may be made without departing from the essence of the invention.Such changes are also implicitly included in the description. Thesechanges still fall within the scope of this invention.

Further, each of the various elements of the invention and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of anyapparatus embodiment, a method embodiment, or even merely a variation ofany element of these. Particularly, it should be understood that as thedisclosure relates to elements of the invention, the words for eachelement may be expressed by equivalent apparatus terms even if only thefunction or result is the same. Such equivalent, broader, or even moregeneric terms should be considered to be encompassed in the descriptionof each element or action. Such terms can be substituted where desiredto make explicit the implicitly broad coverage to which this inventionis entitled. It should be understood that all actions may be expressedas a means for taking that action or as an element which causes thataction. Similarly, each physical element disclosed should be understoodto encompass a disclosure of the action which that physical elementfacilitates. Such changes and alternative terms are to be understood tobe explicitly included in the description.

Having described this invention in connection with a number ofembodiments, modification will now certainly suggest itself to thoseskilled in the art. The example embodiments herein are not intended tobe limiting, various configurations and combinations of features arepossible. As such, the invention is not limited to the disclosedembodiments, except as required by the appended claims.

What is claimed is:
 1. An aircraft electric motor cooling systemcomprising: a) an airflow path through a spinner comprising: i) a firstairflow path between an inner rotor and a stator; ii) a second airflowpath between an outer rotor and the stator; and iii) a third airflowpath along an outer surface of the outer rotor; and b) wherein theairflow path through the spinner comprises a portion extending throughfront stator cooling fins, and wherein the second and third portion arederived at least in part from the front stator cooling fins portion. 2.The system of claim 1, wherein the first airflow path extends alonginner rotor magnets.
 3. The system of claim 2, wherein the secondairflow path extends along outer rotor magnets.
 4. The system of claim2, wherein the first airflow path extends along a front stator yoke andalong a rear stator yoke.
 5. The system of claim 1, wherein the secondairflow path extends along outer rotor magnets.
 6. The system of claim5, wherein the second airflow path extends along a front stator yoke anda rear stator yoke.
 7. The system of claim 1, wherein the first, second,and third airflow paths return to an air stream path.
 8. The system ofclaim 7, wherein the second and third airflow paths extend through arear stator heat sink along with an air stream path.
 9. The system ofclaim 1, wherein the second and third airflow paths extend through arear stator heat sink along with an air stream path.
 10. The system ofclaim 1 further comprising an air stream path extending through a rearstator heat sink.
 11. An electric aircraft motor comprising: a) an innerrotor connected with an outer rotor; b) a stator comprising a windinglocated between the inner rotor and the outer rotor; c) a spinner; d) acooling system comprising: i) an airflow path through the spinnercomprising: (1) a first airflow path between an inner rotor and astator; and (2) a second airflow path between an outer rotor the stator;e) front cooling fins thermally coupled to a front of the stator; f) theairflow path through the spinner extending through the front coolingfins; and g) wherein the front cooling fins are oriented such that thefront cooling fins direct airflow entering spinner radially outwardthrough the front cooling fins.
 12. The motor of claim 11 furthercomprising: a) rear cooling fins thermally coupled to a rear portion ofthe stator; and b) the airflow path through the spinner extendingthrough the rear cooling fins.
 13. The motor of claim 11 furthercomprising rear cooling fins thermally coupled to a rear portion of thestator, the rear cooling fins extending beyond an outer radius of thespinner.
 14. The motor of claim 11 further comprising rear cooling finsthermally coupled to a rear portion of the stator wherein the rearcooling fins are sized so as to extend into an air stream of anaircraft.
 15. The motor of claim 11 further comprising rear cooling finsthermally coupled to a rear portion of the stator wherein the rearcooling fins are sized so as to extend into an air stream of anaircraft.
 16. The motor of claim 11 wherein the first airflow pathextends along inner rotor magnets, and wherein the second airflow pathextends along outer rotor magnets.
 17. The motor of claim 11, whereinthe first airflow path extends along a front stator yoke and along arear stator yoke.
 18. The motor of claim 11, wherein the second airflowpath extends along a front stator yoke and a rear stator yoke.
 19. Amethod for air cooling an electric aircraft motor comprising: a) passingan air flow through a spinner; b) directing a first portion of the airflow to flow between the stator and the inner rotor; c) directing asecond portion of the air flow to flow between the stator and the outerrotor; d) directing a third portion of the air flow to flow along anouter surface of the outer rotor; and e) combining the second and thirdportions of the air flow with an air stream flow and passing thecombined second, third, and air stream flows through a rear stator heatsink.
 20. The method of claim 19, wherein the first portion flows alonginner rotor magnets.
 21. The method of claim 20, wherein the secondportion of the air flow flows along outer rotor magnets.
 22. The methodof claim 20, wherein the first portion flows along a front stator yokeand along a rear stator yoke.
 23. The method of claim 19, wherein thesecond portion of the air flow flows along outer rotor magnets.
 24. Themethod of claim 23, wherein the second portion flows along a frontstator yoke and a rear stator yoke.
 25. The method of claim 19 furthercomprising returning the first, second, and third portions of the airflow to the air stream.
 26. The method of claim 19 comprising directinga front cooling fin portion of the air flow through front stator coolingfins, and wherein the second and third portion are derived at least inpart from the cooling fin portion of the air flow through the spinner.27. The method of claim 19 comprising directing a front cooling finportion of the air flow through front stator cooling fins, and whereinthe second and third portion are derived at least in part from thecooling fin portion of the air flow through the spinner.
 28. An electricaircraft motor comprising: a) an inner rotor connected with an outerrotor; b) a stator comprising a winding located between the inner rotorand the outer rotor; c) a spinner; d) a cooling system comprising: i) anairflow path through the spinner comprising: (1) a first airflow pathbetween an inner rotor and a stator; and (2) a second airflow pathbetween an outer rotor the stator; e) front cooling fins thermallycoupled to a front of the stator; f) the airflow path through thespinner extending through the front cooling fins; and g) rear coolingfins thermally coupled to a rear portion of the stator, the rear coolingfins extending beyond an outer radius of the spinner.
 29. A method forair cooling an electric aircraft motor comprising: a) passing an airflow through a spinner; b) directing a first portion of the air flow toflow between the stator and the inner rotor; c) directing a secondportion of the air flow to flow between the stator and the outer rotor;d) directing a third portion of the air flow to flow along an outersurface of the outer rotor; and e) directing a front cooling fin portionof the air flow through front stator cooling fins, and wherein thesecond and third portion are derived at least in part from the coolingfin portion of the air flow through the spinner.